1. Field of the Invention
This invention relates to an electrophotographic photosensitive member, a process cartridge and an electrophotographic apparatus. More particularly, it relates to an electrophotographic photosensitive member having on a conductive support at least a charge generation layer, a charge transport layer and a protective layer in this order, and a process cartridge and an electrophotographic apparatus which have such an electrophotographic photosensitive member.
2. Related Background Art
In recent years, electrophotographic photosensitive members are required to be made further durable. For example, Japanese Patent Application Laid-open No. 5-173350 discloses that an electrophotographic photosensitive member having very good durability can be provided by forming on a photosensitive layer a protective layer which contains a curable resin. As another example, Japanese Patent Application Laid-open No. 7-5748 discloses what is called injection charging, in which electric charges are injected into a protective layer on a photosensitive layer without being accompanied with any substantial discharge.
Thus, it is one of very important techniques to form a protective layer on the photosensitive layer of an electrophotographic photosensitive member.
Meanwhile, as offices are made small-business and home-operable in recent years, electrophotographic apparatus such as copying machines and printers are required to be made small-size, and electrophotographic photosensitive members have a tendency of being made shorter in length in their generatrix direction.
Since, however, the width of a developing region in the generatrix direction of the electrophotographic photosensitive member depends on the size of a transfer material such as paper, the developing region itself can not be narrowed. Namely, the same paper-feed width or development width must be ensured using a shorter electrophotographic photosensitive member. Accordingly, it has come necessary to form images also in electrophotographic photosensitive member""s end regions in which any images have not been formed in conventional cases.
However, end portions of photosensitive layers or protective layers tend to have non-uniform layer thickness. At the portions having non-uniform layer thickness, charging non-uniformity and sensitivity non-uniformity have tended to occur to make it difficult to form uniform images.
At present, from the viewpoint of good productivity of such layers, what is mostly employed as a coating method therefor is what is called the dip coating, in which a conductive support is plunged into a coating fluid (solution or dispersion) for each layer substantially vertically in the generatrix direction and then lifted up. In such dip coating, however, it has been very difficult to make the layer thickness at an end region equal to that at the middle portion; the former being layer thickness given immediately after the coating fluid for each layer begins to be coated, i.e., the layer thickness on the side where, as the support (cylinder) is lifted up, the coating fluid begins to be coated in the generatrix direction of the electrophotographic photosensitive member layer. This is because it is impossible to prevent the coating fluid perfectly from sagging immediately after the coating.
Especially in the case of the electrophotographic photosensitive member having a protective layer on a photosensitive layer, coating non-uniformity has tended to occur remarkably for the part corresponding to a larger number of layers than an electrophotographic photosensitive member not having any protective layer. Japanese Patent Application Laid-open No. 59-26044 discloses that more uniform images can be obtained by controlling the thickness of the charge generation layer and that of the charge transport layer. It, however, does not disclose any finding at all on the relationship between the protective layer and the photosensitive layer.
To make coating speed higher in order to improve productivity, it is also necessary to lower the concentration of solid content of the coating fluid. However, the coating fluid may more greatly sag with a decrease in the viscosity of the coating fluid, resulting in remarkable occurrence of coating non-uniformity.
Thus, although it is very difficult from the viewpoint of production techniques to obtain good images, it is required to achieve much higher image quality as color-image formation has been achieved in electrophotography and formation of minute images of as high as 1,200 dpi (dot per inch) has been achieved.
An object of the present invention is to provide an electrophotographic photosensitive member having very superior electrophotographic performance, in order to accomplish much smaller size, much lower cost and much higher image quality hereafter, on condition that any coating non-uniformity due to the sagging of coating fluid may occur when the electrophotographic photosensitive member is manufactured.
Another object of the present invention is to provide a process cartridge and an electrophotographic apparatus which have such an electrophotographic photosensitive member.
To achieve the above objects, the present invention provides an electrophotographic photosensitive member comprising a conductive support, and provided thereon a charge generation layer, a charge transport layer and a protective layer in this order, wherein;
the layer thickness a0 (xcexcm) of the charge transport layer at the middle portion of the conductive support in its generatrix direction, the layer thickness b0 (xcexcm) of the protective layer at the middle portion of the conductive support in its generatrix direction, the layer thickness a (xcexcm) of the charge transport layer at a portion other than the middle portion and the layer thickness b (xcexcm) of the protective layer at the portion other than the middle portion satisfy the following expression (1) in a region satisfying 0.8 (xcexcm)xe2x89xa6(a0xe2x88x92a)xe2x89xa63.0 (xcexcm):
b0xc3x97(a/a0)3xe2x89xa6b(xcexcm)xe2x89xa6b0xc3x97(a/a0)1/4xe2x80x83xe2x80x83(1).
The present invention also provides a process cartridge and an electrophotographic apparatus which have such an electrophotographic photosensitive member.